The ultrastructure of small cell lung carcinoma in bronchial biopsy specimens.

Forty-three bronchial biopsy specimens from patients with small cell lung cancer (SCLC) were studied by electron microscopy. In 38 specimens the diagnosis was based on the light microscopic examination of Epon-embedded tissue; 36 of these specimens contained dense-core granules on electron microscopic examination. In five cases the light microscopic diagnosis was either different from the electron microscopic diagnosis or in doubt. Electron microscopy revealed dense-core granules as the only sign of differentiation, and the diagnosis was changed to SCLC. The tumor cell populations in the biopsy specimens were quite heterogeneous. Cells of the oat cell type were always present and, on electron microscopic examination, always showed degenerative changes. It was therefore decided that this cell type represents an artifact. The true SCLC tumor cell, which constitutes only a small portion of the tumor in biopsy specimens, is characterized by a regular oval or rounded cell with pale cytoplasm and a ground-glass nucleus with finely dispersed chromatin. Nucleolated cells, similar to those seen in large cell cancer, are often present but are not ultrastructurally different from nonnucleolated tumor cells.